1. Field of Invention
The invention relates to a scanning device, and more particularly to a scanning device having a flexible pressing member for pressing documents having different thicknesses. The flexible pressing member may be deformed and is arranged such that it is located apart from a transparent platen of the scanning device by a gap.
2. Related Art
In a conventional automatic document feeder, rollers are usually adopted to transport a document onto a scan platen so that a scanning module disposed below the scan platen can capture an image of the document. The depth of field for the image sensor employed in the scanning module is critical to the scan quality of the images generated. Greater the depth of field the image sensor has, the greater tolerance for the distance between the document and the sensor is allowed. Particularly, for the scanner using a contact image sensor (CIS), the image sensor has to be placed extremely close to the paper being scanned in order to obtain a sharp image of the document.
Conventionally, a roller is utilized in a scanner to limit the document transported past the scan window to fall within the range of the depth of field of the scanning module effectively. The roller is in sliding contact with the scan platen. When the document is being transported past the scan window, the roller is in rolling contact with the document, and the document is pressed against the scan platen. In this case, the roller and the scan platen tend to wear off because of the frictional contact there between, which consequently deteriorates the scan quality of the resulting images. In addition, when a thicker sheet of the document is being scanned, the document may not enter the gap between the roller and the scan window for the gap width being smaller than the thickness of the sheet, such that a paper jam may occur and interrupt the scan procedure. Thus, in the prior art, a motion-limiting mechanism is added to the roller for supporting the roller and provides the roller with a track to move up and down. Hence, the gap between the roller and the scan window may be adjusted according to the thickness of the document, and the document may be transported through the gap. However, this mechanism requires more components and the longer assembling time, and the manufacturing cost is inevitably increased.